A database on the fatigue strength of metallic materials was compiled by collecting the experimental fatigue data of the last 20 years in Japan on a nationwide scale as a project in JSMS Committee on Fatigue. In particular attention to statistical fatigue properties, the authors have been analyzing P-S-N characteristics of carbon steels for machine structural use in this database.
When these fatigue data were plotted altogether on S-N coordinates, they were widely dispersed due to a wide range of strength levels of metals. The tensile strength σB was taken up as a typical parameter of the strength level, and the applied stress was normalized by σB. Then all the data were replotted as a σa/σB-N diagram. Thus we have all the data points yielded in a relatively narrow scatter band.
By examining the effects of material and testing conditions on S-N property, it was found that all the S-N plots were successfully classified into the following four groups; (1) S10C-S15C, (2) S20C-S40C, (3) S45C-S58C (Quenched & Tempered), and (4) S45C-S58C (Except for Quenched & Tempered).
Quantitative P-S-N characteristics were finally analyzed for each group based on the stress dependency of the fatigue life distribution. The theoretical results thus obtained were in good agreement with the statistical fatigue properties of respective groups of the materials.
